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For more than 130 years the U.S. Army Corps of Engineers (Corps) has used dikes to "train" the Mississippi River channel and maintain adequate depth for navigation. The Corps relies heavily on these structures--including some with more recent designs--in the Middle Mississippi, between the confluences of the Missouri and Ohio Rivers. Over the past few decades, some researchers have raised concerns about the structures' cumulative impacts on the environment and the height of floodwaters. For the Corps' river training structures in the Middle Mississippi, GAO was asked to examine (1) key requirements and directives that govern their use, (2) how the Corps has addressed key environmental requirements, (3) the extent to which their hydrologic and environmental impacts are monitored, and (4) concerns that researchers have raised about hydrologic and environmental impacts and how the Corps has responded. GAO reviewed relevant laws, regulations, agency documents, and key studies, and interviewed Corps officials and other researchers and experts.

The Corps' authority to use river training structures in the Mississippi River comes from several Rivers and Harbors Acts, which collectively require the Corps to maintain a 9-foot navigation channel in the river, and several Water Resources Development Acts, which also authorize projects in the Corps' civil works program. In using these structures, the Corps must comply with federal environmental laws such as the National Environmental Policy Act (NEPA), the Clean Water Act (CWA), and the Fish and Wildlife Coordination Act, as well as applicable state requirements. The Corps also has its own guidance that district offices are to use when planning, designing, and building river training structures. In using river training structures in the Middle Mississippi, the Corps has addressed some environmental requirements but not all. For example, the Corps has undertaken consultation with other agencies in accordance with the Fish and Wildlife Coordination Act. However, the Corps has not complied with certain requirements of NEPA or CWA. For example, in constructing new river training structures the Corps has continued to rely on an environmental impact statement prepared in 1976. Even though significant changes have occurred in the river and in the Corps' design of its structures, it has not prepared the additional analyses required by NEPA to assess whether further environmental impact analysis is warranted. Similarly, the Corps has not obtained the appropriate CWA permits or state water quality certifications for river training structures as required. The Corps routinely assesses some of the hydrologic impacts of its Middle Mississippi training structures but not the environmental impacts. For example, the Corps has performed physical and numerical modeling to assess the hydraulic impacts of proposed structures prior to construction, and it has routinely monitored the hydrologic impacts after construction through data collection and observation of the river's surface elevation (known as river stage). The Corps has also analyzed the relationship between river stage and the volume and speed of river flow (known as discharge), looking for rising or falling trends that might indicate whether the structures are having a cumulative effect during floods. The Corps, however, does not routinely monitor the environmental impacts of its structures after construction, although it has conducted studies to monitor impacts on certain endangered species, such as the pallid sturgeon, and on fish and wildlife habitats. Researchers have highlighted two key areas of concern with river training structures--degradation of river habitat and increased flooding. Although the Corps has attempted to address the habitat concerns, the agency and some researchers disagree over flooding concerns. In response to the habitat concerns, the Corps has modified some river training structures to increase flows between them, and has begun installing newer types of structures in select locations to promote aquatic habitat. Regarding flooding, the Corps disagrees with the concern that its structures have led to an increase in river stage during high flow events, and has undertaken various studies that support its position. Nevertheless, significant professional disagreement remains over this issue, which many experts believe could be resolved through additional physical and/or numerical modeling. GAO recommends that the Department of Defense direct the Corps to prepare an environmental assessment for river training structures in the Middle Mississippi, obtain required water quality permits for new structures, and conduct physical and/or numerical modeling to assess the cumulative impact of structures on flood heights. The department generally agreed with these recommendations.

Recommendations for Executive Action

Status: Closed - Implemented

Comments: In July 2012, the Department of Defense reported that the Army Corps of Engineers' St. Louis District initiated an environmental assessment of river training structures for the Mississippi River between the Ohio and Missouri Rivers Regulating Works Project in November 2011. The department further reported that preparation of the environmental assessment is ongoing and scoping meetings were held in January and February of 2012. In relation with another GAO recommendation to review existing NEPA documentation, the Corps took a "hard look" at the 1976 EIS to determine if a supplement was warranted. The Corps concluded that there was significant new information and circumstances that bear on the potential impacts of the project on the environment. As a result, in September 2013 the Corps transitioned from producing an EA to producing an SEIS . Notice of the SEIS was made in the Federal Register in December 2013, and a scoping report for the SEIS was issued in April 2014. The Corps issued the draft SEIS in November 2016, and the final SEIS in May 2017.

Recommendation: To help ensure compliance with NEPA, the Secretary of Defense should direct the Chief of Engineers and Commanding General of the U.S. Army Corps of Engineers to prepare an environmental assessment (EA) to determine, in accordance with Council on Environmental Quality and Corps regulations, whether there are significant new circumstances or information relevant to the Middle Mississippi navigation project's environmental concerns that have emerged since publication of the 1976 environmental impact statement (EIS), and if so, prepare a supplemental EIS (SEIS) in accordance with NEPA, or if not, prepare a finding of no significant impact in accordance with NEPA.

Agency Affected: Department of Defense

Status: Closed - Implemented

Comments: In July 2012, the Department of Defense reported that the environmental assessment being prepared pursuant to our first recommendation, and subsequent documents prepared under NEPA for specific projects, will include site-specific impact assessments of new river training structures in accordance with the Army Corps of Engineers' Regulation 200-2-2: Procedures for Implementing NEPA. In April 2014, the Corps issued environmental assessments of site-specific impacts for three new river training structure projects.

Recommendation: To help ensure compliance with NEPA, the Secretary of Defense should direct the Chief of Engineers and Commanding General of the U.S. Army Corps of Engineers to develop and present in the EA an approach to ensure that site-specific impacts are assessed, as appropriate, for new river training structures in the Middle Mississippi.

Agency Affected: Department of Defense

Status: Closed - Implemented

Comments: In response to our report, the Department of Defense (DOD) stated that the Army Corps of Engineers (Corps) would review and revise District procedures for implementing NEPA, as needed, to ensure that existing Corps regulations and policies are properly followed and documented. In July 2012, DOD stated that the St. Louis District Engineer had evaluated the District's procedures to ensure they are in compliance with applicable laws and Corps regulations and that, as a result, in May 2012, the District Engineer signed the Commander's policy to ensure environmental compliance.

Recommendation: To help ensure compliance with NEPA, the Secretary of Defense should direct the Chief of Engineers and Commanding General of the U.S. Army Corps of Engineers to review and revise as needed St. Louis District procedures to ensure that determinations of whether existing NEPA documents need to be supplemented are performed in accordance with Corps regulations implementing NEPA and documented.

Agency Affected: Department of Defense

Status: Closed - Implemented

Comments: The Corps sought state water quality certifications for four river training structure projects from the Illinois EPA and Missouri Department of Natural Resources. The Illinois and Missouri departments approved the certifications for all four projects between November 2013 and January 2014. The Corps issued CWA Section 404 permit equivalents for three of the four projects. According to Corps officials, the Corps voluntarily delayed work on one project pending the outcome of additional numerical modeling, and compliance with Section 404 will be obtained before proceeding.

Recommendation: To help ensure compliance with CWA, the Secretary of Defense should direct the Chief of Engineers and Commanding General of the U.S. Army Corps of Engineers to obtain CWA Section 404 permit-equivalents and state water quality certifications as required for new river training structures in the Middle Mississippi.

Agency Affected: Department of Defense

Status: Closed - Implemented

Comments: The Corps completed two studies of the impacts of river training structures in the Middle Mississippi River. A physical model study conducted at the University of Iowa was completed in December 2012 and a numerical model study conducted at the University of Illinois was completed in May 2013. In addition, the Corps submitted two articles to the American Society of Civil Engineers Journal of Hydraulics on the impacts of river training structures in the Middle Mississippi River. These articles were peer-reviewed and published in October 2013.

Recommendation: To help resolve concerns over river training structures' cumulative effect on river stages during periods of high flow, the Secretary of Defense should direct the Chief of Engineers and Commanding General of the U.S. Army Corps of Engineers to conduct physical or numerical modeling, or some combination thereof, to provide further insight into the relative magnitude of this effect for flood conditions on the Middle Mississippi. The Corps should determine and conduct the appropriate level of review for such modeling under its Civil Works Review Policy, including consideration of independent external peer review.